1. Technical Field
The field of the invention relates to engine systems using pressure sensors. In particular, the field of the invention relates to systems that use a determination of barometric pressure.
2. Background of the Invention
In engine control systems, it is advantageous to provide an estimate of atmospheric (barometric) pressure. Barometric pressure (BP) affects engine exhaust back-pressure, which affects the residual burnt exhaust gas remaining in the cylinder at the close of the exhaust valve. Further, barometric pressure affects available manifold vacuum for operating various accessories.
One method for estimating barometric pressure uses measured and predicted mass airflow. In this system, a difference between these two values is first attributed to temperature, and the remaining difference is attributed to a change in barometric pressure. Such a system is described in U.S. Pat. No. 5,136,517.
The inventors herein have recognized several disadvantages with the above system. In particular, such an estimation method can be expensive to calibrate such that accurate measurements are provided over all operation conditions. In addition, the inventors have recognized that improved engine control can be achieved if accurate barometric pressure readings are provided throughout vehicle operation. Thus, even if an initial accurate barometric pressure is available, it is difficult to provide an accurate barometric pressure throughout vehicle operation.
The above disadvantages of prior approaches are overcome by a method for estimating atmospheric pressure surrounding an engine intake manifold coupled to an orifice, with a first gauge sensor coupled upstream of the orifice and a second absolute sensor coupled downstream of the orifice. The method comprises indicating whether flow through the orifice is substantially zero; and determining atmospheric pressure based on the upstream gauge pressure sensor and the downstream absolute pressure sensor in response to said indication.
By using both a gage and an absolute pressure sensor, it is possible to provide an accurate barometric pressure. Further, since such a measurement can be made whenever flow is substantially zero, it is possible to provide periodic updates during vehicle operation. Thus, in one example, where the flow is a recirculated exhaust flow, the barometric pressure update can be provided during, for example, idling, or wide open throttle operation since EGR is typically discontinued in these conditions. However, it should be noted that there are various other methods for indicating when flow through the orifice is substantially zero, such as, for example, based on operating condition, based on environmental conditions, or any other method. Further, it should be noted that there are various ways to determine atmospheric pressure based on the upstream gauge pressure sensor and the downstream absolute pressure sensor. For example, atmospheric pressure can be determined base on the sum or difference between the upstream and downstream sensor, or a mathematical relationship using both the upstream and downstream sensor can be used.
An advantage of the above aspect of the invention is improved engine control, thus giving reduced emissions.